Patent GB-879714-A (GB)
Title: Improvements relating to automatic control mechanisms and analogue computing mechanisms therefor
Inventor: MACDONALD ALEXANDER TORRENCE
IPC: G05B19/4105
Filed: 1957-01-09
Abstract: 879,714. Electric copying machines. ELECTRIC & MUSICAL INDUSTRIES Ltd. Jan. 9, 1958 [Jan. 9, 1957], No. 818/57. Class 38 (6). [Also in Group XXXVI] A computing system provides output signals representing a locus to be followed by a cutter of a machine tool cutting a profile and the direction of said locus in response to incremental signals #x #y derived from interpolators, said signals being in the form of phase-modulated carrier waves which are recorded, e.g. on magnetic tape for use in the automatic machine tool control system. The X and Y signals are modified by #x, #y (Fig. 1) to compensate for the cutter radius R in the embodiment of Fig. 3. In the computer (Fig. 2) the interpolator output signals #x, #y amplitude modulate a carrier wave and are applied to stator windings 3, 4 of a resolver having a principal rotor winding 5 and a secondary quadrature rotor winding 6 on the same shaft, a rotor winding 7 of a second resolver also being mounted on this shaft. In response to signals on 3, 4 motor 11 tends to maintain rotor 5 and therefore rotor 7 at an angle # (see Fig. 1), rotor 7 (at an angle # to stator 8) receiving an A.C. carrier signal A sin # c t so that the outputs across windings 8, 9 are proportional to A sin # c t. cos #, A sin # c t sin # respectively and are retarded and advanced by capacitor 13 resistor 14 to produce a phase-modulated carrier signal A sin (# c t+ ##) the phase of which is a function of # and the signal, together with signals A sin (# c t + #x), A sin (# c t + #y) and A sin # c t are recorded on the tape, representing the x and y coordinates of the cutter axis position and the carrier frequency signal respectively. The derivation of the x, y signals is similar to that of the # signal. A machine tool control system is shown in Fig. 3, and the signals from the tape are reproduced by the transducer 17. Signal A sin (# c t + ##) is compared with the signal induced in the resolver rotor 31 by stator signals sin # c t, cos # c t, that is with sin (# c t + #) (where # = angle of rotor 31 to stator 32) in a phase discriminator 25, a motor 28 moving rotor shaft 31 until the phase difference is zero when #= #. Rotor 34 coupled to rotor 31 is therefore also set at angle # to its stator 35, the rotor being fed with a carrier signal sin # c t of amplitude R (the cutter radius) so that the signals induced in 36, 35 will be (R sin #) sin # c t, (R cos #) sin # c t respectively. The latter is fed to one input of an amplitude comparison unit 38 of an A.M. modulated carrier system servo loop where it is compared with a signal from a position analogue unit representing the rotor position 44, the rotor therefore being rotated by motor 41 until the inputs to 38 are equal when the angle of rotor 44 is equal to ##x (R cos #) which is proportional to the required correction #x. Resolver stators 45, 46 are supplied with signals sin [# c t + #x), cos (# c t + #x) from 19, 22 respectively so that the output from rotor 44 is a phase-modulated signal sin (# c t + #x + ##x). The y-phase modulated signal sin (# c t + #y + ##y) is similarly derived from stator 36, and resolver 49. In a modification (Fig. 4, not shown), an additional interpolator feeds a value of # to a computing circuit for each set of #x, #y values a signal corresponding to A sin (# c t + ##) being derived by an amplitude comparison unit and a feedback loop including an analogue position indicator and a servomotor to set the rotor of a resolver at an angle # to one stator winding. Alternative phasemodulating resolvers ...to replace (31, 32, 33) and (44, 45, 46) or (48, 49, 50) of .Fig. 3 are described (Figs. 5a, 5b, not shown). Specifications 796,994, 803,627, 830,462 and 863,114 are referred to.